1. Field of the Invention
The present invention relates to a semiconductor pressure sensor.
2. Description of the Related Art
Conventional pressure sensor semiconductor substrates are produced by the following procedure.
First, an oxide film that has a predetermined thickness is formed on one surface of a first semiconductor substrate that is constituted by a single-crystalline silicon substrate, and a penetrating aperture that has an aperture direction that is oriented in the thickness direction of the oxide film is formed by removing a portion of the oxide film. Next, a recess portion that has an inner peripheral surface that is flush with an inner peripheral surface of the penetrating aperture is formed on the first semiconductor substrate. Next, a second semiconductor substrate that is constituted by a single-crystalline silicon substrate is bonded to the first semiconductor substrate by means of an oxide film so as to cover the penetrating aperture that is exposed on the surface of the oxide film. A diaphragm is formed on a portion of the second semiconductor substrate that faces the recess portion by reducing thickness of the second semiconductor substrate, and finally a conventional pressure sensor semiconductor substrate is produced by forming a strain detecting element on a surface of the diaphragm (see Patent Literature 1, for example).    Patent Literature 1: Japanese Patent No. 4214567 (Specification)
In conventional pressure sensor semiconductor substrates, positions of opening edge portions of the recess portion that is formed on the first semiconductor substrate and positions of edge portions of the penetrating aperture that is formed on the oxide film are aligned. Now, residual stresses arise in the oxide film, but magnitudes of the stresses that result from the residual stresses that act on the oxide film are discontinuous at the edge portions of the penetrating aperture. When pressure is applied to the diaphragm from outside, and the diaphragm flexes, large stresses arise at the opening edge portions of the recess portion. If the positions of the opening edge portions of the recess portion and the positions of the edge portions of the penetrating aperture are aligned, as in conventional pressure sensor semiconductor substrates, stresses that are discontinuous at the boundary of the edge portions of the penetrating aperture are superimposed on the stresses that arise in the diaphragm as the diaphragm flexes. Breakage pressure tolerance of the diaphragm when pressure is applied to the diaphragm from outside is reduced significantly because of this.